The present invention relates in general to electronic circuits and particularly concerns the comparator circuits commonly used in electronic circuits. It has been developed with particular attention to its possible use for producing monolithic comparator circuits with precision hysteresis and high input impedance.
There is a particular need for comparators with these characteristics in order to produce interfaces between sensors with variable reluctance (for example, sensors used to detect the speed and position of the shaft of an internal combustion engine in a motor vehicle) and the corresponding processing circuits (for example, in the case of the sensors mentioned above, the electronic control unit of the engine).
For use in such a situation, the comparator must detect a signal the level of which (for example 100 mV), in some situations, is little greater than a lower limit level (for example, 50 mV) below which no detection should take place. There is therefore a need for a comparator which has the broadest possible hysteresis so that it is substantially insensitive to noise (which is present to a considerable extent in an automotive environment) but which, at the same, can ensure operation in the limit condition indicated above, taking account of the spread of the hysteresis value, both as regards its absolute value and in relation to temperature. Moreover, a further input impedance is also required to prevent errors due to the high resistances of the sources which drive the comparator.